Whether it be on replaceable blades or blades meant to be re-sharpened, e.g., a cutter bar for a sickle mower, every cutting edge has a relatively short useful life because the sharp cutting edge is worn or dulled whenever it collides with an obstacle. Eventually, the wear progresses to a point where the cutting edge no longer cuts, but rather knocks off (fractures) portions of the material the blade collides with.
Whether worn blades are to be replaced or sharpened, some dismantling and reassembly of the cutting machine is required. Those skilled in the art will appreciate how time-consuming frequent changing of the cutting blades can be.
German Patent DE-PS 221 144, describes a blade shape for replaceable blades for mowing equipment in which a number of grooves angularly disposed and lying parallel to one another are arranged on the bottom of the blade to provide a saw-like cutting edge.
As a result of wear, this blade's cutting edge becomes more saw-like with the result that sharpening is not necessary. That is to say, wear on the thin material in the area of the indentations creates a form of saw-teeth, as shown in FIG. 4 of the German Patent, which first grab the material to be cut, e.g., blades of grass, and then tear through them. Even though reference is made to a blade here, a saw is in fact what is described. The disadvantages of a saw are well-know: in the case of fresh green material, the blades are soon clogged with cutting debris, deformations can also result.
U.S. Pat. No. 3,382,654 describes a cutter bar for sickle mowers which is made of plastic. Plastic parts of lower wear-resistance are inserted in recesses on the cutting edge of this cutter bar. In contrast to the instant invention, these inserts form a continuous cutting edge when placed in their corresponding recesses and do not leave any areas of low thickness of material.
As a result of (uneven) wear on the plastic inserts having lower wear-resistance, the cutting edge creates a saw-tooth edge. As noted above, a disadvantage of saw-tooth cutting action is the accumulation of debris that blocks the cutting edge. It must also be stated that this prior art invention does not take into account the facts that the parts of low wear resistance are very quickly dulled, the final cutting is done by a sharp exposed point and that such devices are expensive to manufacture.